I agree with the points above except point no. 10. I don't remember the problem you specified, especially of being constantly kicked out of dialogue. As far as i know you could escape a dialogue and cut off or finish early a line of dialogue of particular character with a simple right mouse click.

Other things i would preferred:

1) The game HUD could be improved; less distracting border art around every interface objects, including the character inventory and alchemy making screens. They could use some more streamlining.

2) Adding a interesting and recruit-able companion(s) with different skills and personalities. I think it's not easy to implement and probably effect the currently state of gameplay too much. Valve did well with incoporating the Alyx character into plot and various aspects of gameplay.

3) Reduce the amount of different alchemy potions, if not, re-balance or redesign them as currently i almost use only swallow, cat and couple other potions, the rest are pretty useless.

4) Spells; same as in 3) above = Reduce/re-balance or redesign the types of spells. I think the wind and fire spells are more useful, and you could ignoring all other types of spells.